Pointiness for edge mask doesn't work at all
Subdivide the cube. It requires more geometry to be displayed. &quot;Dirty Vertex Colors&quot; in Vertex Paint mode works the same way if you want to mask out edges and corners.
EDIT: No wait I just realised what's wrong. You should move the color stop sliders in the ColorRamp node more to the left. Tried setting it up like yours and it's all black here as well. Try 0.515 for the black stop's position.